In certain high speed rotating equipment with static excitation, such as large turbine-generator systems, carbon brush current collection systems are utilized in conducting a field current to the generator rotor. The collector sets typically comprise a pair of collector rings, or one for each pole, mounted on the rotor and a set of stationary brushes angularly displaced around, and in contact with, each collector ring. In order to protect the collector sets and to prevent inadvertent contact with them by personnel, they are usually housed within an enclosure which includes a fixed base. This enclosure is commonly referred to as a collector house. Typically the collector house includes stationary traverse end walls having sealed openings through which the rotor shaft passes and a house defining the roof and sidewalls of the enclosure. In some installations, it is desirable to be able to change the brushes without shutting down the generator. Accordingly, the housing is provided with doors through which access may be gained to the collector set.
Because of high energy demands, it is common to arrange several carbon brushes within a magazine or gang type brush holder. Several brushes, normally six, are grouped within the brush holder, a plurality of which are arranged around the outside diameter of the generator rotor. Examples of such brush holders are described in U.S. Pat. Nos. 3,387,155, issued on June 4, 1968, and U.S. Pat. No. 3,710,478 which issued on Jan. 16, 1973.
While these devices permit ease of brush replacement, it must first be determined when one or more brushes has become worn to the point that it must be replaced. This is typically done by a visual inspection of the brushes on a periodic basis. Such inspections are done while the generator is on-line, in order to minimize the down time of the power generation system. Thus, an inspector, in order to visually inspect for worn brushes, must enter a relatively hostile environment while the generator is operating. Difficulty can arise in visually inspecting those brushes disposed on the interior of the brush holder, due to their location with respect to the outer brushes. What is needed then is a device whereby a worn brush condition can be easily viewed by an operator so as to allow for a quick determination of any worn brush condition.
Application Ser. No. 388,890, filed on Aug. 3, 1989, describes a means for remotely determining when one or more carbon brushes within a ganged brush holder has worn down a predetermined amount. Briefly, a strip of electrically-conductive material is secured to the holder and configured so as to be electrically insulated from the holder when a new brush is inserted into the holder. The strip contacts the brush by means of a finger having an insulated knob such that, when the brush has worn a predetermined amount, the knob disengages the brush so that the finger is caused to contact the brush holder. A light emitting diode, electrically connected to the strip and located at a remote location, is then illuminated to indicate the worn brush condition. The above-referenced application is assigned to the present assignee and is hereby incorporated by reference.